1. Field of the Invention
This invention relates to a process for producing bis-(N-N-dialkylamino)alkyl ethers of the formula (R.sub.2 NR').sub.2 O, where R is a methyl or ethyl group and R' is a bivalent alkylene group having from 2 to 3 carbon atoms. These ethers are useful as catalysts in the production of polyurethanes, especially cellular polyurethanes.
2. Description of the Prior Art
Bis[beta(N,N-dimethylamino)alkyl] ethers, including the commercially important bis[2-(N,N-dimethylamino)ethyl] ether ("BDMEE"), are known to be valuable polyurethane catalysts, particularly in the production of flexible polyurethane foam. By way of illustration, the production of polyurethane foam by reacting an organic isocyanate with an active hydrogen-containing compound (polyol) in the presence of a bis[beta-(N,N-dimethylamino)alkyl] ether catalyst is disclosed in U.S. Pat. No. 3,330,782.
Several processes for the production of bis[beta (N,N-dimethylamino)ethyl] ethers, including BDMEE, are known. One process utilizes di(2-chloroethyl) ether as a reactant as disclosed in U.S. Pat. Nos. 3,400,157 and 3,426,072. However, there are several disadvantages associated with the use of di(2-chloroethyl) ether, including (a) the need to employ comparatively expensive corrosion resistant equipment because of the presence of chlorides in the reaction mixture, (b) disposal problems associated with by-product chlorides, and (c) the relatively high cost and lack of ready availability of di(2-chloroethyl) ether. Another process for the production of bis[beta-(N,N-dimethylamino)alkyl] ethers involves reacting a beta-(N,N-dimethylamino) alkanol, a beta-(N,N-dimethylamino) alkyl chloride and an alkali metal hydroxide using a modified Williamson synthesis as disclosed in U.S. Pat. No. 3,480,675. However, this modified Williamson synthesis has several disadvantages, including (a) several solids-handling steps, (b) a discontinuous mode of operation, (c) disposal problems associated with by-product sodium chloride, and (d) one of the reactants, 2-dimethylaminoethyl chloride, used in the production of BDMEE is an unstable liquid and is also a vesicant which requires special handling. A further process for the production of BDMEE comprises reacting trimethylamine with 2-[2-(N,N-dimethylamino)ethoxy] ethanol in the presence of a nickel catalyst under super-atmospheric pressure as disclosed in U.S. Pat. No. 3,957,875. However, this process requires the use of a costly high-pressure reactor and provides product yields that leave room for improvement. Accordingly, it is desirable to provide a process for the production of bis-(N,N-dialkylamino)alkyl ethers, including BDMEE, that does not possess the disadvantages associated with the above-mentioned processes.